Over more than three decades, various gas bearing slider designs (e.g. air bearing sliders) have been created in an attempt to solve the problem of fly height variation. While there is no generally agreed upon single "figure of merit" for an air bearing slider, it is undeniable that it should, at least, have the following qualities: low stiction; low take-off and landing speeds; a low sensitivity of fly height to skew angle variations (i.e. angle between the central axis of the slider and the axis of movement of the recording media); and a low sensitivity of fly height to disk speed variations and to manufacturing errors, such as crown (a distortion of the slider). For magnetic recording purposes, constancy of recording gap is important, even in the presence of disturbing mechanical excitations, e.g., disk roughness, spindle run-out, aerodynamic buffeting, etc.
The prior art evidences a number of techniques for attempting to overcome the aforementioned effects and disturbances. U.S. Pat. No. 3,197,751 to Felts shows a flying magnetic head assembly wherein a generally planar slider has a recording head mounted behind its trailing edge. The recording head is positioned so that it penetrates an air film over the disk and maintains that position irrespective of moderate variations of angle of attack between the slider and the disk surface. The leading edge of the slider is rounded or beveled to provide a "ski nose" to enable air to be compressed beneath the slider.
U.S. Pat. No. 3,573,768 to Harris illustrates an air bearing slider that includes a pair of stepped regions, one upstream from another. The two level steps enable a low stiction line contact between the slider body and the recording surface when the recording surface is at rest. Further, as a result of the height difference between the steps, no taper is required of the step surfaces. The distance between the front and rear steps is indicated as being approximately equal to the desired flying height of the slider. Harris states that this distance should be approximately 50 microinches.
Chang et al. in U.S. Pat. No. 5,021,906 disclose a programmable air bearing slider which includes the separated front and rear air bearing surfaces, separated by a central non-air bearing region. The central region is recessed and includes a piezoelectric element that is capable of deforming the slider. The front air bearing surface includes a tapered leading portion (approximately 10 milliradians) and the rear air bearing surface has no taper angle. By appropriate control of the piezoelectric element, a curvature is induced in the central region thereby lowering the fly height of a head attached to the rearmost portion of the slider.
Matthews in U.S. Pat. No. 4,605,977 discloses another version of an active-control air bearing slider. In this instance, however, Matthews employs a railed slider with a piezoelectric element that enables a lead taper angle of the slider to be adjusted to achieve a desired flying height.
A widely used air bearing slider configuration includes a body with a pair of rails that are oriented parallel to the direction of movement of the recording surface. The aerodynamics of a railed slider make its fly height particularly susceptible to skew angle variations. With the popularity of rotary arm actuators, much attention has been given to reducing the effects of skew on railed sliders. Railed sliders also exhibit strong, so-called side leakage of air from beneath the rails. As side leakage varies with disk speed, undesirable variations in fly height of the slider occur as disk speed varies from inner to outer disk tracks. Furthermore, railed sliders generally exhibit large front taper angles that substantially affect a slider's speed dependence.
In U.S. Pat. No. 4,870,519 to White, a railed air bearing slider assembly is described wherein each rail has a tapered forward end to provide a converging inlet to achieve a fluid air film beneath the rails. Additionally, each rail has at least one longitudinal angled contour to compensate for skew. Additional description of the structure described by White can be found in "An Air Bearing Slider With Uniform Flying Height and Fast Take-Off Characteristics", Tribology and Mechanics of Magnetic Storage Systems, Volume III, ASLE Special Publication SP-21, American Society of Lubrication Engineers, Park Ridge, Ill. pages 95-101.
In U.S. Pat. No. 4,673,996, to White, a slider is described in which the loss of lift of a slider due to skew is compensated by steps on the slider's side rails. The step height is typically adjusted to a precise value to achieve a fly height of a desired type (such as a flat profile) under steady flying conditions. This principle was given the name TPC ("Transverse Pressure Contour"). Sliders of the TPC type are typically highly speed sensitive and are also sensitive to skew variations that result from the angular velocity of an actuator arm.
Clifford et al in "An Air Bearing Minimizing the Effects of Slider Skew Angle", IEEE Transactions on Magnetics, Volume 25, September 1989, pages 3713-3715, describe a further technique for reducing skew effects in a railed slider assembly. Clifford et al suggests the use of transverse slots across both rails which function as pressure relief areas to enable achievement of a more uniform fly height. Other pressure relief structures in railed air bearing sliders can be found in U.S. Pat. No. 4,802,042 to Strom.
Other shaped air bearing sliders that employ rails may be found in "Magnetic Head With Aero-Shaped Air Bearing Surface" by Balster et al., Research Disclosure, Jan. 19, 1991, number 321; U.S. Pat. Nos. 4,984,114 to Takeuchi et al; 4,218,715 to Garnier; 4,984,740 to Chhabra et al.; 4,734,803 to Nishihira and 5,062,017 to Strom et al.
U.S. Pat. No. 4,757,402 to Mo discloses a slider assembly with a circular bearing pad that presents a substantially equal cross sectional area to an air film moving with media even when the slider is skewed relative to the oncoming air film.
As above indicated, a slider with narrow rails is very sensitive to skew. Sliders actuated by linear actuators rarely are subject to more than 10.degree. of skew. In disk drives that use rotary actuators, however, the skew angle can be as large as 20.degree.. When an air bearing slider of the standard taper/flat configuration is used with a rotary actuator, the actuation arm is generally tangent to the disk's inner data tracks. This leads to a long actuator arm with considerable inertia.
While the prior art describes how various slider configurations can be designed to cope with the problems of skew, it generally does not address the question of minimizing speed and skew dependence, together. Typically, prior art sliders have taper angles of 10 milliradians or larger. At such large taper angles, a slider's aerodynamic lift decreases with increasing taper angle (i.e. in aeronautical parlance, a "stall" regime). The tapers of most prior art sliders operate in the stall regime in that they employ a large taper angle. The primary reason is for manufacturing ease in that it is easier to assure that the intersection formed by the juncture of slider's taper and flat regions ends up at the correct location when the taper angle is large. However, a cost of such a high taper angle is that in the stall regime, lift becomes highly speed dependent, even at normal operating speeds.
A further problem with a large taper angle is that at medium and high disk speeds, air is regurgitated from the taper region. As a result, a sliders' taper regions are exposed to relatively large amounts of contaminated air which never enter the flat rail sections of the slider. This may cause debris accretion in the taper area that contributes to head crashes since it modifies the shape of the air bearing in the crucial entry region.
Accordingly, it is an object of this invention to provide an improved air bearing slider for magnetic recording.
It is another object of this invention to provide an improved air bearing slider that avoids the problem of regurgitated air from the slider's taper region.
It is yet another object of this invention to provide an improved air bearing slider that is less sensitive to skew.
It is yet another object of this invention to provide an improved air bearing slider structure which exhibits low stiction, low take-off and landing speeds, a fly height that is substantially insensitive to skew and disk speed variations, and a substantial insensitivity to slider crown variations.